Mybatis框架使用基础

说明：
（1）内容基础，主要用于展示配置过程
（2）展示了使用配置类和只使用映射文件的不同过程，说明mybatis的内部工作原理
（3）所使用的mysql的数据：https://www.jianshu.com/p/fcf340f79a87

1. pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>cn.johnyu</groupId>
    <artifactId>mybatis-demo</artifactId>
    <version>1.0-SNAPSHOT</version>

    <dependencies>
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.7</version>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.26</version>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.18.20</version>
            <scope>provided</scope>
        </dependency>
        <dependency>
            <groupId>org.junit.jupiter</groupId>
            <artifactId>junit-jupiter-api</artifactId>
            <version>5.7.2</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.junit.jupiter</groupId>
            <artifactId>junit-jupiter-engine</artifactId>
            <version>5.7.2</version>
            <scope>test</scope>
        </dependency>

    </dependencies>
</project>

2. resources/mybatis-conf.xml

此文件引入另外两个文件：
(1) 同级下的mysql.properties存放的数据的连接信息
(2) 和EmployeeMapper.xml,存放Employee的映射信息

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    <properties resource="mysql.properties"></properties>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="${driver}"/>
                <property name="url" value="${url}"/>
                <property name="username" value="${username}"/>
                <property name="password" value="${password}"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="cn/johnyu/mapper/EmployeeMapper.xml"/>
    </mappers>

</configuration>

mysql.properties文件内容：

username=root
password=123
url=jdbc:mysql://localhost:3306/scott
driver=com.mysql.cj.jdbc.Driver

3. src/main/resources/cn/johnyu/mapper/EmployeeMapper.xml

重点说明：
（1）此文件并没有存储位置和文件名称的假设，可以存储于可以由mybatis-conig.xml找到的任意位置。
（2）namespace和 id,在不使用反射机制和动态代理的情况下，也没有任何的假设

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="xxx">
    <select id="loadEmployee" resultType="cn.johnyu.pojo.Employee">
        select empno as id,ename,job from emp where empno=#{id}
    </select>
</mapper>

4. 实体类和测试类：

Employee.java

//cn/johnyu/pojo/Employee.java
package cn.johnyu.pojo;

import lombok.Data;

@Data
public class Employee {
    private Integer id;
    private String ename;
    private String job;
}

MainApp(不使用反射和动态代理)

package cn.johnyu;

import cn.johnyu.pojo.Employee;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import java.io.IOException;

public class MainApp {
    public static void main(String[] args) throws IOException {
        SqlSessionFactoryBuilder builder=new SqlSessionFactoryBuilder();
        SqlSessionFactory factory= builder.build(Resources.getResourceAsReader("mybatis-conf.xml"),"development");
        //线程不安全
        try(SqlSession session=factory.openSession()){
            Employee employee=(Employee) session.selectOne("loadEmployee",7369);
            System.out.println(employee.getEname());
        }
    }
}

5. 生成动态代理的mapper:

(1) 改进后的EmployeeMapper.xml：

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">

<mapper namespace="cn.johnyu.mapper.EmployeeMapper">
    <select id="load" resultType="cn.johnyu.pojo.Employee">
        select empno as id,ename,job from emp where empno=#{id}
    </select>
</mapper>

此时的namespace和id分别指向了mapper接口和相应的方法名称
(2) EmployeeMapper接口：

package cn.johnyu.mapper;

import cn.johnyu.pojo.Employee;
import org.apache.ibatis.annotations.Mapper;

@Mapper
public interface EmployeeMapper {
     Employee load(Integer id);
}

(3) mybatis-conf.xml文件的变化：

    <mappers>
<!--    可以指定包名，或者具体类名-->
<!--        <package name="cn.johnyu.mapper"/> -->
        <mapper class="cn.johnyu.mapper.EmployeeMapper"/>
    </mappers>

(3) 测试类的变化：

package cn.johnyu;

import cn.johnyu.mapper.EmployeeMapper;
import cn.johnyu.pojo.Employee;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import java.io.IOException;

public class MainApp {
    public static void main(String[] args) throws IOException {
        SqlSessionFactoryBuilder builder=new SqlSessionFactoryBuilder();
        SqlSessionFactory factory= builder.build(Resources.getResourceAsReader("mybatis-conf.xml"),"development");
        //线程不安全
        try(SqlSession session=factory.openSession()){
            EmployeeMapper mapper = session.getMapper(EmployeeMapper.class);
            Employee employee = mapper.load(7369);
            System.out.println(employee.getEname());
        }
    }
}

接续阅读： springboot与mybatis整合技术